1. Field of the Invention
The present invention relates to an intermediate transfer belt to form a toner image on a photoreceptor and transfer the toner image to a transfer medium, and an image forming apparatus using the same.
2. Description of Related Art
As a tandem-type color image forming apparatus, there exists a system where a toner image on a photoreceptor drum is superimposed onto an intermediate transfer belt and transferred to a transfer medium. In order to improve transferability to a transfer medium, an intermediate transfer belt that can handle surface irregularity of a transfer medium with its multilayer structure has been proposed as the intermediate transfer belt used for this system.
In an intermediate transfer belt as mentioned above, a reinforcing layer, a middle layer and a surface protection layer are stacked in order, and the reinforcing layer and the surface protection layer are formed on the surface of the intermediate transfer belt. In general, the reinforcing layer is made of a resin film such as polyimide (especially, toughened polyimide) and polyvinylidene-fluoride (PVDF). The middle layer is made of nitrile rubber (NBR), silicon, urethane or the like. The surface protection layer is coated with fluorine, Teflon (registered trademark) or the like.
Japanese Unexamined Patent Publication No. 10-39642 proposes a technique that defines the characteristics of a reinforcing layer and the strength characteristics of an elastic layer. Japanese Unexamined Patent Publication No. 2004-101675 proposes that when an intermediate transfer belt is stretched on a given roller in an image forming apparatus, a reinforcing layer contacting the roller has larger surface resistance than a value of volume resistance of the whole belt, thereby preventing applied current or applied voltage (hereinafter referring only to applied current) for transferring a toner image to an intermediate transfer belt from running into the roller.
Recently, an image forming apparatus has been required to be smaller and higher-speed. For this reason, in a tandem-type image forming apparatus, a plurality of image forming units are required to be disposed at a smaller interval.
However, when an interval between image forming units is made smaller to meet this requirement, the problem is that in the aforementioned conventional intermediate transfer belt, electric current applied to transfer a toner image to an intermediate transfer belt passes through the surface of the intermediate transfer belt to another image forming unit and therefore it is impossible to put proper electric charge (voltage) on the intermediate transfer belt.